Pebble heater



July l0, 1951 H. J. HEPP ETAL PEBBLE HEATER Filed Sept. 27, 1946 N @FiOmmm Qmmu

m .Sanoma om IN V EN TORS H. J. HEPP BY M. O. KILPATRICK ATTCRNEYSPatented July 10, 1'95 UNITED" STATES 'T OLF F l CE 2,559,957 I PBLE HFRHaroldJ. Hepp and Myron Kilpatrick, Battles- ,v

ville, Okla., assignors` to Phillips Petroleum Company, a" corporationof Delaware l Autsiitmter 27, 1946; seiaiN. 99,666

clanes'. (C1. 19e-55) This --inventi'on relates uto an improvedtpiocessandapparatus for effecting" thermal reactionsin vapor phase bycontactingthe vapors'jvv'ithiV ot refractory pebbles;y IAspecilicembodimjento l invention pertains `to amethodfand-apparatu's orintroducingVl hot pebbles tol thefreactioiizone fa pebble'heaterrAnother embodiment is concerned' with a methodF off withdrawing' product*ga-sfv from there'actionzone. U l y A Themethodandl apparatusn hereindisclosed have!` application topractically' alljpebble heater processesbutarefparticularly' adapted to pr esses' for the-conversion of*Vhydrocarborro'ilss` as"-the`rnal cracking; dehydrogenation," arcnrnatr--y zation, reforming, and the liker Thelinv'entiofn exhibits itsgreatest utilityin high temperature thermal crackingv of hydrocarbonsin'th'e range of about14oo3ooo F; l

yet no entirely satisfactory pebble heater process for crackinghydrocarbons hasbeen'i de'- vised.l In order'tov understandsomefo'fthe'difculties of the prior art andthe contributionsof thisinvention 1 thereto," reference'l is rrade" tof the; drawing ofi whichFigure :1 is'an elvational'view, partly in; section, of'aconveiltionalpebbl'e'heater apparatus. Figures V:2;and 3 are elevationalviews," partly in section ,dogfV *two preferreddesigns ofp'ebbleheaterjeactors acordingto the invention;A

heatef practice, mamontiguous, `mass of refractoryv pebbles desc Y S@1109511 pebblelleatellll. and isV therein'convtacted withacquntercurrent stream',

or'hdt' gas, Usualliffeeinbllsiin gars admitted;

providingvaporhspace 3ll above the bed. Simule.

to reaction temperature by contact With5hot pebbles I0 land desirable;conversion Vist effected before theeiliuents are taken offv throughlines I8.

Feeddistributing means I 'I is constructed-to pro vide 'uniformdistribution of vfeedl gases Without" unduly obstructing the ow ofpebbles: Eiuents* in'fline' I8' are taken through a quenchingstepand/orprodu'ct separation step as-'desiredr-"As" thefinas's ofpebblesdescendsthroughreactor" I5 itis cooled to belowreaction'temperature' and" of repose between must be reheate'd before furtherutiliiat'ion Pebbles pass out' through outlet I9, vfeeder valve 2 5',and chute 22 into elevator 23 which lifts theiii to a point above pebbleheating chamber IIV and, drops them into chute' 24 from which they flowthrough inlet Zeinto heating chamber I I.

It is desirable to maintain relatively equal gas pressures in'v chambersII and I5`to' prevent'w of gases from` one chamber to the' other. Iiisome cases'it is desirable to admitste'am through linesit, 2l, and 28toY prevent'escape of gases fromtho'se chambers through pebble lines, v

The term pebbleas' referred to throughout the specification is definedas any particulate *reifractory contact materialw'hich is readily owablethrough a contact chamber. Pebbles are preferably spherical and fromabout' 1/8 inch vto l inch inA size but'spheres rangingin size fromabout '1A' inch to" 1/2 inch arey the'inost praeti'cal'. Uniform shapesand sizes arepreferred but pebbles of irregular shape and size may beused. Pebbles' may be madeV of 'ceramic material, such as alumina, or ofmetals" and alloys, such as iron; nickel, Monel and Yinconel.`

Using thermal cracking asv an illustration tem-'- pera'tures'of. 1500to' 2500 F. are maintained .in chamber I5. l. VIn this conventionalsystem just, described a throat connecting `the two chambers is axiallylocated and projects into the reaction chamber thereby formingapebble-freevapor. space'at the top of the vessel. With thisr design. aAgreat dealof trouble has been encountered 'on` account of the formationof carbon on the throatl and other areas in this region since it isalmost impossible to avoid somedeadspaces or regions wherethe'gas flowis relatively low. In' addition, the' high temperature of the throatitself com-- pared to thatofthe gases aggravates the carbonformingAtendency since the throat is in contact with the partially/'crackedgases.

In the'present'inventi'on the two described are avoided by placingfthethroat inian,

unsymrnetrical'positioir at the side of thechamber as shown vin Figures`2 vand 3.Y invention provides a'smooth streamlined which is free of'obstruction and deadr spaces",` thus greatly reducing the'tendency toform 'carbon.`r Moreover, the vgases dor not come in contact" withasuper 'heatedthroat This design also profvides for a substantially equaltransit time for all portionsofthe gas 'leaving different partsof the'pebble Abed in 'its Apassage to the quench` zone.`

It is an' object 'of' thepresent invention" to pr'o'` vide 1animprovedpebbleheater reactor designg1 It is also an object of thepresent" inventioto'" The design of the l' gas exitx provide a pebbleheater reactor which effects more uniform conversion of hydrocarbonwithout concomitant deposition of carbon on the pebble throat. Anotherobject of the invention is to provide a pebble heater reactor designwhich effects uniform withdrawal of reaction products from the pebbleheater bed. A further object of the invention is to provide a processfor effecting improved hydrocarbon conversions in a pebble heater. Otherobjects of the invention will become apparent from the accompanyingdisclosure.

Referring more in detail to the design of Figure 2, reactor I has apebble inlet or neck I4, positioned tangentially internally to thereactor (the cross section of both heater and throat being circular).Conical bottom 29 serves as a hopper for feeding pebbles into pebbleoutlet I9. Feed line I6 entering the lower part of reactor I5 is incommunication with feed distribution means I'I. The top closure wall ofreactor I5 converges gradually and smoothly into product outlet I3. Thisfeature provides for relatively equal transit time for gases between allparts of the top surface of the pebble bed and the duct leading to thequenching means. The pebbles in bed I form a sloping top surface due tothe natural angle of repose of the pebbles. This provides anunsymmetrical vapor space 3I and to overcome this, outlet I8 iseccentric to the cross section of reactor I5. In order to provide forequal transit time of gases through the pebble bed I0, gas distributingmeans Il is positioned parallel to pebble bed surface 20. Lines 21 and28 admit steam to prevent the escape of feed and reaction products fromreactor I5 thru either pebble passageway.

Figure 3 shows a slight modification of the reactor shown in Figure 2,the essential difference being the location of neck I4. Neck I4 istangent externally to reactor I5 and is in communication therewith thruthe cylindrical wall thereof. Gas outlet I8 provides for horizontaltake-off as compared to the oblique take-off in Figure 2.

Numerous modifications of the invention are feasible. While a reactorwith a circular cross section is most desirable, other regular shapessuch as square, octagonal, hexagonal, and so forth may be used. Theadvantages of the invention accrue from placing pebble inlet or neck I4in other positions near the periphery of the reactor. Instead of asingle product outlet a multiple-point exit header may be utilized withthe individual outlets so positioned that each takes off a proportionateshare of the gas.

In the operation of a reactor, such as that shown in Figures 2 and 3, ina pebble heater installation, a mass of pebbles heated to well above thereaction temperature desired in reactor I5 descends through neck I4,forms a pebble bed IB, filling the reactor up to a level 2U. As the hotpebbles slowly descend through the reactor and passout through pebbleexit I9, they are contacted with a desirable feed introduced throughline I6 and distribution means I'I. The ascending feed is quicklybrought to reaction temperature and is converted to desirable productsaccording to a predetermined set of conditions. The reaction productsconverge in vapor space 3| passing into outlet I8 from which they areconducted to a rapid quench. Pebbles descending through outlet I9 areconsiderably cooler than those introduced through neck I8 and areconducted by an elevator to a point above the pebble heating unit forreheating and again passing through the reactor.

In hydrocarbon conversion reactions at elevated temperatures in whichcarbon is normally deposited on the pebble throat of a conventionalpebble heater reactor, carbon deposition is substantially eliminated inthe design of the invention. Moreover, the uniform and rapid Withdrawalof reaction products from the top of the pebble bed effected by thedesign of the invention materially increases the yield of desirableproducts.

Various modifications of the invention not described will becomeapparent to those skilled in the art. The illustrative details disclosedare not to be construed as imposing unnecessary limitations on theinvention.

We claim:

l. A conversion chamber for reacting gases at elevated temperatures bydirect contact with a gravitating mass of pebbles and rapidlywithdrawing reaction products before further appreciable reactionoccurs, which comprises an upright, cylindrical vessel having anoblique, convex, curvilinear top closure member generally conforming tothe natural slope of a freely flowing bed of pebbles introduced throughan inlet at the juncture of said member with the cylindrical side ofsaid vessel at the highest point thereof; an open pebble inlet in saidvessel at said point; a gas outlet conduit in said closure memberdisposed so that a normal drawn from the midpoint of the top surface ofsaid bed of pebbles passes therethrough said outlet conduit graduallydiverging into the contour of said closure member so as to streamlinegas flow out of said chamber; a bottom closure member for said vesselhaving an open pebble outletl therein encompassing the axis of saidvessel; and gas inlet means extending completely across the lowerportion of said vessel so as to distribute gas uniformly over the entirecross section thereof.

2. Apparatus of claim 1 in which the conduit means for introducingpebbles to said cylindrical- Walled vessel is externally tangentthereto.

3. Apparatus of claim 1 in which the conduit means for introducingpebbles to said cylindricalwalled vessel is internally tangent thereto.

4. In a process for conversion of hydrocarbon involving cracking whereinhydrocarbon vapor is passed upwardly through a conned upright verticallyextending zone in intimate contact with a gravitating bed of hot,refractory, pebbles introduced into the upper portion of said zone andflowing out the bottom'thereof, thereby heating and at least partiallycracking said hydrocarbon, and an eiiluent hydrocarbon stream subject todegradation reactions with concomitant carbon deposition is removed fromthe upper portion of said zone, the improvement which comprisescontinuously introducing said pebbles to said zone through an inlet atthe juncture of its upper and lateral boundaries, thereby forming andmaintaining a top surface on said pebble bed conforming to the naturalslope thereof and oblique to the axis of said zone, and continuouslyfunneling the cracked eiiluent through a zone of gradually and uniformlydecreasing volume in the direction of flow to a vapor outlet oppositethe center of the top surface of said pebble bed so as to decrease theaverage residence time of said eiuent in the upper portion of said zoneand reduce the formation of carbon therein.

5. A process for the conversion of hydrocarbon comprising passing asuitable hydrocarbon in vapor phase upwardly through a gravitating bedof hot, refractory pebbles in direct contact therewith in an uprightcylindrical zone under reaction conditions so as to convert saidhydrocarbon to more desirable hydrocarbon subject to degradationreactions with concomitant carbon deposition at conversion temperature;continuously in- C troduoing a contiguous stream of hot refractory Jpebbles to said zone at the confluence of the cylindrical side with thetop thereof so as to form and maintain a pebble bed having an obliquetop surface extending from the point of pebble ,s introduction along thenatural repose of said pebble bed to the opposite side of said zone;Withdrawing reaction effluent from the top surface of said pebble bedthrough a vapor space gradually and uniformly decreasing in Volume inthe direction of vapor flow to an outlet opposite the center of the topsurface of said pebble bed so as to streamline and funnel the flow ofeiuent from the Zone, the point of pebble introduction and the funnelingof eiliuent from said Zone cooperating to reduce stagnant gas space inthe upper end of said zone and concomitant carbon deposi- A tiontherein.

HAROLD J. HEPP. MYRON O. KILPATRICK.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS

4. IN A PROCESS FOR CONVERSION OF HYDROCARBON INVOLVING CRACKING WHEREINHYDROCARBON VAPOR IS PASSED UPWARDLY THROUGH A CONFINED UPRIGHTVERTICALLY EXTENDING ZONE IN INTIMATE CONTACT WITH A GRAVITATING BED OFHOT, REFRACTORY, PEBBLES INTRODUCED INTO THE UPPER PORTION OF SAID ZONEAND FLOWING OUT THE BOTTOM THEREOF, THEREBY HEATING AND AT LEASTPARTIALLY CRACKING SAID HYDROCARBON, AND AN EFFLUENT HYDROCARBON STREAMSUBJECT TO DEGRADATION REACTIONS WITH CONCOMITANT CARBON DEPOSITION ISREMOVED FROM THE UPPER PORTION OF SAID ZONE, THE IMPROVEMENT WHICHCOMPRISES CONTINUOUSLY INTRODUCING SAID PEBBLES TO SAID ZONE THROUGH ANINLET AT THE JUNCTURE OF ITS UPPER AND LATERAL BOUNDARIES, THEREBYFORMING AND MAINTAINING A TOP SURFACE ON SAID PEBBLE BED CONFORMING TOTHE NATURAL SLOPE THEREOF AND OBLIQUE TO THE AXIS OF SAID ZONE, ANDCONTINUOUSLY FUNNELING THE CRACKED EFFLUENT THROUGH A ZONE OF GRADUALLYAND UNIFORMLY DECREASING VOLUME IN THE DIRECTION OF FLOW TO A VAPOROUTLET OPPOSITE THE CENTER OF THE TOP SURFACE OF SAID PEBBLE BES SO ASTO DECREASE THE AVERAGE RESIDENCE TIME OF SAID EFFLUENT IN THE UPPERPORTION OF SAID ZONE AND REDUCE THE FORMATION OF CARBON THEREIN.